From tropos to atropos: 5,5′-bridged 2,2′-bis(diphenylphosphino)biphenyls as chiral ligands for highly enantioselective palladium-catalyzed hydrogenation of α-phthalimide ketones

A class of atropisomeric diphosphine ligands with a wide range of dihedral angles has been developed. X-ray study of the Pd(II) complexes of these ligands showed that as the bridge length increased, the dihedral angles and the ligand bite angles increased as well, while an excessive increase in bridge length had a reverse effect. It was found that there was a correlation between the ligand dihedral angles and the enantioselectivity in Pd-catalyzed asymmetric hydrogenation of α-phthalimide ketones, and excellent enantioselectivities of up to 99% ee were afforded.